Two Periods of Skarn Mineralization in the Baizhangyan W–Mo Deposit,Southern Anhui Province,Southeast China: Evidence from Zircon U–Pb and Molybdenite Re–Os and Sulfur Isotope Data          下载免费PDF全文

Chunhai Li  Yaohui Jiang  Guangfu Xing  Kunyi Guo  Chao Li  Minggang Yu  Peng Zhao  Zheng Wang 《Resource Geology》2015,65(3):193-209

The recently discovered Baizhangyan skarn‐porphyry type W–Mo deposit in southern Anhui Province in SE China occurs near the Middle–Lower Yangtze Valley polymetallic metallogenic belt. The deposit is closely temporally‐spatially associated with the Mesozoic Qingyang granitic complex composed of g ranodiorite, monzonitic g ranite, and alkaline g ranite. Orebodies of the deposit occur as horizons, veins, and lenses within the limestones of Sinian Lantian Formation contacting with buried fine‐grained granite, and diorite dykes. There are two types of W mineralization: major skarn W–Mo mineralization and minor granite‐hosted disseminated Mo mineralization. Among skarn mineralization, mineral assemblages and cross‐cutting relationships within both skarn ores and intrusions reveal two distinct periods of mineralization, i.e. the first W–Au period related to the intrusion of diorite dykes, and the subsequent W–Mo period related to the intrusion of the fine‐grained granite. In this paper, we report new zircon U–Pb and molybdenite Re–Os ages with the aim of constraining the relationships among the monzonitic granite, fine‐grained granite, diorite dykes, and W mineralization. Zircons of the monzonitic granite, the fine‐grained granite, and diorite dykes yield weighted mean U–Pb ages of 129.0 ± 1.2 Ma, 135.34 ± 0.92 Ma and 145.3 ± 1.7 Ma, respectively. Ten molybdenite Re–Os age determinations yield an isochron age of 136.9 ± 4.5 Ma and a weighted mean age of 135.0 ± 1.2 Ma. The molybdenites have δ³⁴S values of 3.6‰–6.6‰ and their Re contents ranging from 7.23 ppm to 15.23 ppm. A second group of two molybdenite samples yield ages of 143.8 ± 2.1 and 146.3 ± 2.0 Ma, containing Re concentrations of 50.5–50.9 ppm, and with δ³⁴S values of 1.6‰–4.8‰. The molybdenites from these two distinct groups of samples contain moderate concentrations of Re (7.23–50.48 ppm), suggesting that metals within the deposit have a mixed crust–mantle provenance. Field observation and new age and isotope data obtained in this study indicate that the first diorite dyke‐related skarn W–Au mineralization took place in the Early Cretaceous peaking at 143.0–146.3 Ma, and was associated with a mixed crust–mantle system. The second fine‐grained granite‐related skarn W–Mo mineralization took place a little later at 135.0–136.9 Ma, and was crust‐dominated. The fine‐grained granite was not formed by fractionation of the Qingyang monzonitic granite. This finding suggests that the first period of skarn W–Au mineralization in the Baizhangyan deposit resulted from interaction between basaltic magmas derived from the upper lithospheric mantle and crustal material at 143.0–146.3 and the subsequent period of W–Mo mineralization derived from the crust at 135.0–136.9 Ma.  相似文献   

Geochemical and oxygen isotope signatures of mantle corundum megacrysts from the Mbuji-Mayi kimberlite,Democratic Republic of Congo,and the Changle alkali basalt,China     

《Comptes Rendus Geoscience》2015,347(1):24-34

Oxygen isotope signatures of ruby and sapphire megacrysts, combined with trace-element analysis, from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China, provide clues to specify their origin in the deep Earth. At Mbuji-Mayi, pink sapphires have δ¹⁸O values in the range 4.3 to 5.4‰ (N = 10) with a mean of 4.9 ± 0.4‰, and rubies from 5.5 to 5.6‰ (N = 3). The Ga/Mg ratio of pink sapphires is between 1.9 and 3.9, and in rubies, between 0.6 and 2.6. The blue or yellow sapphires from Changle have δ¹⁸O values from 4.6 to 5.2 ‰, with a mean of 4.9 ± 0.2‰ (N = 9). The Ga/Mg ratio is between 5.7 and 11.3. The homogenous isotopic composition of ruby suggests a derivation from upper mantle xenoliths (garnet lherzolite, pyroxenite) or metagabbros and/or lower crustal garnet clinopyroxenite eclogite-type xenoliths included in kimberlites. Data from the pink sapphires from Mbuji-Mayi suggest a mantle origin, but different probable protoliths: either subducted oceanic protolith transformed into eclogite with δ¹⁸O values buffered to the mantle value, or clinopyroxenite protoliths in peridotite. The Changle sapphires have a mantle O-isotope signature. They probably formed in syenitic magmas produced by low degree partial melting of a spinel lherzolite source. The kimberlite and the alkali basalt acted as gem conveyors from the upper mantle up to the surface.  相似文献   

祁连山新生代古海拔变化的碳氧同位素记录     

戚帮申  胡道功  杨肖肖  张绪教  赵希涛 《地球学报》2015,36(3):323-332

祁连山构成青藏高原的北东边界,是研究青藏高原的隆升与向内陆扩展的关键区域,利用新生代湖相沉积的碳氧同位素组成估算祁连山古海拔对认识青藏高原的隆升有重要意义。在中祁连陆块不同地点出露的始新统、渐新统、中新统和中晚更新统分别取样并进行碳氧同位素分析,估算相应地质时期的古年均温和古海拔高度。结果表明,祁连山地区古近纪的海拔约为2711 m,中新世早期的海拔为2848 m左右,中新世中晚期祁连山海拔达到约3586 m,中晚更新世祁连山的古海拔约为3790~3890 m。古近纪祁连山的海拔较低,但已经构成了青藏高原的东北边界;中新世中晚期祁连山强烈隆升,形成了盆-山构造地貌格局;第四纪祁连山地壳重新活跃并呈阶段性快速隆升,河流堆积和侵蚀交替进行。根据碳氧同位素估算的祁连山古海拔高度变化为认识青藏高原隆升的过程提供参考。  相似文献   

中天山卡瓦布拉克杂岩带中闪长岩的锆石U-Pb年龄及Hf同位素特征   总被引：1，自引：0，他引：1  

尼加提?阿布都逊  木合塔尔?扎日  吴兆宁 《吉林大学学报(地球科学版)》2015,(6):1702-1712

卡瓦布拉克杂岩带出露于中天山地块东段卡瓦布拉克—阿克塔格地区,沿卡瓦布拉克断裂呈东西向展布。笔者选择构成该杂岩带的中—基性岩石主体闪长岩,开展了LA-ICP-MS锆石U-Pb年代学和LA-MC-ICP-MS锆石Hf同位素研究。结果表明:闪长岩中锆石呈自形—半自形,发育典型的岩浆锆石振荡生长环带,Th/U值较高(均大于0.40),且Th、U含量呈现较好的正相关关系,为典型的岩浆成因锆石;这些锆石的206Pb/238 U年龄加权平均值为(375±1)Ma,MSWD=0.081,属晚泥盆世,可代表其结晶年龄;锆石具有较均一的Hf同位素组成,初始比值为0.282 655~0.282 747、εHf(t)值为4.0~7.2,其对应的亏损地幔模式年龄为714~842Ma。结合区域地质资料认为,卡瓦布拉克杂岩带中的闪长岩由亏损岩石圈地幔发生部分熔融而形成。  相似文献   

Integrated biostratigraphy and carbon isotope stratigraphy of the Lower Cretaceous (Barremian to Albian) Adriatic-Dinaridic carbonate platform deposits in Istria, Croatia     

Blanka Cvetko Tešovi?  Bosiljka Glumac 《Cretaceous Research》2011,32(3):301-324

The Adriatic-Dinaridic carbonate platform (ADCP) was one of the largest and relatively well preserved Mesozoic platforms in the Mediterranean region (central Tethys). The peninsula Istria, in the northwestern part of the ADCP, is built up predominantly of shallow-water carbonates of the Middle Jurassic (Dogger) to Eocene age and, to a lesser extent, of Paleogene clastic deposits (flysch and calcareous breccia). This study focuses on a Lower Cretaceous (Barremian to Albian) succession of strata at five localities in western Istria. Stratigraphic determinations are based on identification of nine microfossil assemblages (benthic foraminifera and calcareous algae Dasycladales) and on using their taxa as index fossils. The age of strata with these microfossil assemblages, however, is questionable. Most of the age uncertainties are associated with a regional emersion, which occurred on the ADCP during the Aptian or close to the Aptian-Albian transition. It is unclear what portions of the Upper Aptian and/or Lower Albian are missing along this unconformity. A stable isotope study was conducted on homogenous micritic matrix samples in an attempt to resolve some of these uncertainties. Variations in carbon isotope compositions proved useful for stratigraphic correlation between the examined successions of strata, for improving their age determination, and for relating them to other coeval successions that span an important time interval of major oceanographic changes and carbon-cycle perturbations associated with the Early Aptian oceanic anoxic event (OAE 1a).  相似文献   

西藏谢通门县邦弄含铁电英岩脉的地质特征及成因分析   总被引：1，自引：0，他引：1  

夏祥标  郑来林  李军敏  李再会 《矿床地质》2011,30(4):742-748

文章介绍了西藏谢通门县邦弄地区含铁电英岩脉的地质特征.电英岩脉的延伸方向大致与区内的断层平行,围岩为中粒斑状角闪黑云二长花岗岩.电英岩脉中见有不同程度的铁矿化,共有23条矿化较好的含铁电英岩脉.含铁电英岩脉中矿石矿物为赤铁矿(镜铁矿),脉石矿物为石英、电气石及少量的白云母和长石.矿石具叶片状、鳞片状结构,块状构造,矿石...  相似文献   

云南个旧白沙冲和北炮台花岗岩岩石学、地球化学研究及成因探讨   总被引：1，自引：0，他引：1       下载免费PDF全文

李肖龙  毛景文  程彦博 《地质论评》2011,57(6):825-836

白沙冲岩体和北炮台岩体均位于个旧矿田的东区北段.白沙冲岩体岩性主要为黑云母花岗岩,而北炮台岩体岩性主要为似斑状黑云母花岗岩.本文通过对白沙冲岩体、北炮台岩体进行岩石学、地球化学、Nd、Sr同位素研究,厘定白沙冲岩体属过铝质的高钾钙碱性花岗质岩石,北炮台岩体属准铝质的钾玄岩系列花岗岩.两岩体均表现出亏损Ba、Sr、Nb、...  相似文献   

Geology,mineral chemistry and tourmaline B isotopes of the Córrego Bom Sucesso area,southern Serra do Espinhaço,Minas Gerais,Brazil: Implications for Au–Pd–Pt exploration in quartzitic terrain     

Alexandre Raphael Cabral  Bernd Lehmann  Miguel Tupinambá  Michael Wiedenbeck  Michael Brauns 《Journal of Geochemical Exploration》2011

The Palaeo-Mesoproterozoic metasiliciclastic rocks of the southern Serra do Espinhaço, Minas Gerais, Brazil, are host to historically important alluvial deposits of diamonds and gold. Detrital gold grains often comprise Au–Pd–Pt intermetallic compounds, with low Ag contents, which contain inclusions of tourmaline and titaniferous hematite (up to ~ 6 wt.% TiO₂). The latter minerals connect the alluvial mineralisation to the rutile–hematite–quartz veins and tourmalinisation observed in the quartzitic country rocks of the alluvial gravel. The quartzite (Sopa-Brumadinho Formation of lacustrine to fan-deltaic origin) is affected by pervasive B metasomatism with F-bearing tourmaline replacing the recrystallised quartz fabric. The tourmaline belongs to the alkali group, with Mg/(Mg + Fe) and X/(X + Na) ratios in the ranges from 0.5 to 0.7 and 0.18 to 0.29, respectively, where X represents vacancies in the X site. Boron-isotopic values of tourmaline vary from ~ 1 to − 10.4‰ δ¹¹B. The B-isotope range, in conjunction with the Na–Mg-rich tourmaline composition, and the widespread occurrence of tourmalinite in the Sopa-Brumadinho Formation suggest a derivation from non-marine evaporitic brines. Brines are capable of transporting otherwise immobile Ti and explain, under oxidising conditions, the fractionation of Ag from Pd to precipitate palladiferous gold with extremely high Pd/Ag ratios. Zirconium-in-rutile and Ti-in-quartz temperatures for a variety of hematite-rich veins suggest episodic vein emplacement over a temperature range from around 500 °C to ~ 350 °C. Cross-cutting relationships and episodic vein emplacement indicate a late-Brasiliano age.  相似文献   

The Rumuruti chondrite group     

Addi Bischoff  Nadia Vogel  Julia Roszjar 《Chemie der Erde / Geochemistry》2011,(2):101-133

Since 1994, the Rumuruti (R) chondrites have been recognized as a new, well-established chondrite group differing from carbonaceous, ordinary, and enstatite chondrites. The first R chondrite, Carlisle Lakes, was found in Australia in 1977. Meanwhile, the number has increased to 107 (December, 2010). This group is named after the Rumuruti meteorite, the first and so far the only R chondrite fall. Most of the R chondrites are breccias containing a variety of different clasts embedded in a clastic matrix. Some textural and mineralogical characteristics can be summarized as follows: (a) the chondrule abundance in large fragments and in unbrecciated rocks is ∼35–50 vol%; (b) Ca,Al-rich inclusions are rare; (c) the olivine abundance is typically 65–78 vol%; (d) the mean chondrule diameter is ∼400 μm; (e) in unequilibrated R chondrites, low-Ca pyroxene is dominating, whereas in equilibrated R chondrites it is Ca-rich pyroxene; (f) the typical olivine in a metamorphosed lithology is ∼Fa_38–40; (g) matrix olivine in unequilibrated, type 3 fragments and rocks has much higher Fa (∼45–60 mol%) compared to matrix olivines in type 4–6 lithologies (∼Fa_38–41); (h) spinels have a high TiO₂ of ∼5 wt%; (i) abundant different noble metal-bearing phases (metals, sulfides, tellurides, arsenides) occur. The exception is the metamorphosed, type 5/6 R chondrite La Paz Icefield 04840 which contains hornblende, phlogopite, and Ca-poor pyroxene, the latter phase typically occurring in low-grade metamorphosed R chondrites only.In bulk composition, R chondrites have some affinity to ordinary chondrites: (a) the absence of significant depletions in Mn and Na in R chondrites and ordinary chondrites is an important feature to distinguish these groups from carbonaceous chondrites; (b) total Fe (∼24 wt%) of R chondrites is between those of H and L chondrites (27.1 and 21.6 wt%, respectively); (c) the average CI/Mg-normalized lithophile element abundances are ∼0.95 × CI, which is lower than those for carbonaceous chondrites (≥1.0 × CI) and slightly higher than those for ordinary chondrites (∼0.9 × CI); (d) trace element concentrations such as Zn (∼150 ppm) and Se (∼15 ppm) are much higher than in ordinary chondrites; (e) the whole rock Δ¹⁷O of ∼2.7 for R chondrites is the highest among all meteorite groups, and the mean oxygen isotope composition is δ¹⁷O = 5.36 ± 0.43, δ¹⁸O = 5.07 ± 0.86, Δ¹⁷O = +2.72 ± 0.31; (f) noble gas cosmic ray exposure ages of R chondrites range between ∼0.1 and ∼70 Ma. More than half of the R chondrites analyzed for noble gases contain implanted solar wind and, thus, are regolith breccias. The 43 R chondrites from Northern Africa analyzed so far for noble gases seem to represent at least 16 falls. Although the data base is still scarce, the data hint at a major collision event on the R chondrite parent body between 15 and 25 Ma ago.  相似文献   

Multi-proxy approach (H/H, O/O, C/C and Sr/Sr) for the evolution of carbonate-rich groundwater in basalt dominated aquifer of Axum area, northern Ethiopia     

Tewodros Alemayehu  Albrecht Leis  Anton Eisenhauer  Martin Dietzel 《Chemie der Erde / Geochemistry》2011,(2):177-187

Isotopic and chemical composition of groundwater from wells and springs, and surface water from the basalt-dominated Axum area (northern Ethiopia) provides evidence for the origin of water and dissolved species. Shallow (depth < 40 m) and deep groundwater are distinguished by both chemical and isotopic composition. Deep groundwater is significantly enriched in dissolved inorganic carbon up to 40 mmol l⁻¹ and in concentrations of Ca²⁺, Mg²⁺, Na⁺ and Si(OH)₄ compared to the shallow type.The δ²H and δ¹⁸O values of all solutions clearly indicate meteoric origin. Shifts from the local meteoric water line are attributed to evaporation of surface and spring water, and to strong water–rock interaction. The δ¹³C_DIC values of shallow groundwater between −12 and −7‰ (VPDB) display the uptake of CO₂ from local soil horizons, whereas δ¹³C_DIC of deep groundwater ranges from −5 to +1‰. Considering open system conditions with respect to gaseous CO₂, δ¹³C_DIC = +1‰ of the deep groundwater with highest PCO₂ = 10^−0.9 atm yields δ¹³C_CO2(gas) ≈ −5‰, which is close to the stable carbon isotopic composition of magmatic CO₂. Accordingly, stable carbon isotope ratios within the above range are referred to individual proportions of CO₂ from soil and magmatic origin. The uptake of magmatic CO₂ results in elevated cations and Si(OH)₄ concentrations. Weathering of local basalts is documented by ⁸⁷Sr/⁸⁶Sr ratios of the groundwater from 0.7038 to 0.7059. Highest values indicate Sr release from the basement rocks. Besides weathering of silicates, neoformation of solids has to be considered, which results in the formation of, e.g., kaolinite and montmorillonite. In several solutions supersaturation with respect to calcite is reached by outgassing of CO₂ from the solution leading to secondary calcite formation.  相似文献